In general, plasma, an ionized gas, is the fourth state of matter that is not solid, liquid, and gas. Free electrons, positive ions, neutral atoms, and neutral molecules coexist and incessantly interact with each other in plasma. The control of each component and concentration is of significance. In engineering aspects, plasma is regarded as gas that can be formed and controlled by an external electric field.
A conventional plasma generating apparatus is described below.
As shown in FIG. 1, a conventional plasma generating apparatus is configured to generate plasma 18 by installing two plate electrodes that are a source electrode 11 and an ESC (or a susceptor) 12 such that they are spaced a predetermined distance apart up/down within a vacuum chamber 10, then placing a substrate 17 on a top surface of the ESC 12, and then applying an external Radio Frequency (RF) and forming a strong electric field between the source electrode 11 and the ESC 12.
Non-described reference numerals 13, 14, 15, and 16 denote a source RF, a bias RF, a source matcher, and a bias matcher, respectively.
In the conventional, so-called Capacitively Coupled Plasma (CCP) type plasma generating apparatus, uniform plasma can be generated even for a large-scale target by using a plate capacitor.
However, in the CCP type plasma generating apparatus, a density of plasma generated is low and, particularly, there is a disadvantage that it is difficult to generate and maintain plasma at a low pressure of 10 mTorr (mT) or less despite the fact that there is a demand for a low pressure process of 10 mT or less due to the recent mini-authorization in a semiconductor process and a Liquid Crystal Display (LCD) process.
Also, there is a disadvantage in that the low plasma density leads to a reduction of an etch rate and a deposition rate, thus deteriorating productivity.
As shown in FIG. 2, a conventional plasma generating apparatus is configured to generate plasma 28 by placing a substrate 23 on a top surface of an ESC (or a susceptor) 22 within a vacuum chamber 21, applying a bias RF 24, applying a source RF 27 to an antenna 26 that is disposed on a top surface of a ceramic vacuum plate 25 that covers a top surface of the vacuum chamber 21, inducing a flow of electric current, applying a magnetic field to the interior of the vacuum chamber 21, forming an inductive electric field by the applied magnetic field, and accelerating electrons by the inductive electric field.
Non-described reference numerals 24a and 27a denote a bias matcher and a source matcher, respectively.
In the conventional, so-called Inductively Coupled Plasma (ICP) type plasma generating apparatus, plasma can be advantageously generated at high density compared to the CCP type and also, high-density plasma can be generated even at a low pressure of 10 mT or less at which the CCP type could not do so. Thus, the ICP type has been widely used in a semiconductor process needing the characteristic of low pressure.
However, in the ICP type, it is difficult to obtain a uniform plasma density because a potential difference exists between both an RF power application terminal and the ground terminal for the outflow of electric current that are isolated.
In the ICP type, there is a disadvantage that if the antenna is installed within the chamber, arcing occurs because a strong electric potential is formed at a front end (a part to which RF is applied) of the antenna.
Also, in the ICP type, if the antenna is inserted into the chamber, serious contamination may occur because the antenna is formed of copper (Cu) to reduce impedance of the antenna.
In recent years, semiconductor wafers have been large-sized to 300 mm beyond 200 mm and are henceforth expected to be more large-sized to a diameter of 450 mm. So, plasma uniformity is of much importance. However, the ICP type has a limitation in achieving the large-sizing of diameter and also, has a difficulty in ensuring large-scale plasma uniformity despite the fact that the large scale plasma uniformity has to be more guaranteed for an LCD device than a semiconductor.
In order to overcome such drawbacks, the ICP type keeps a distance between the ESC and the ceramic vacuum plate wide. This leads to an increase of a stay time of a reaction gas injected into the chamber. The thus increasing stay time of the injected reaction gas causes an increase of an ionization rate of gas and thus formation of complex kinds of radicals compared to the CCP type. Thus, there is a disadvantage the ICP type does not conform to the recent semiconductor and LCD process having to control delicate radicals.
The ICP type can generate uniform plasma at a low pressure at which plasma diffusion works well compared to the CCP type, but there is a problem that the ICP type cannot generate uniform plasma at a high pressure of 100 mT to 10 T at which plasma diffusion works poor.